U.S. patent application number 14/766936 was filed with the patent office on 2015-12-31 for method for transmitting discovery signal for device-to-device communication in wireless communication system and apparatus therefor.
This patent application is currently assigned to LG ELECTRONICS INC.. The applicant listed for this patent is (LG ELECTRONICS INC.). Invention is credited to Hanbyul SEO.
Application Number | 20150382389 14/766936 |
Document ID | / |
Family ID | 51428497 |
Filed Date | 2015-12-31 |
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United States Patent
Application |
20150382389 |
Kind Code |
A1 |
SEO; Hanbyul |
December 31, 2015 |
METHOD FOR TRANSMITTING DISCOVERY SIGNAL FOR DEVICE-TO-DEVICE
COMMUNICATION IN WIRELESS COMMUNICATION SYSTEM AND APPARATUS
THEREFOR
Abstract
A method for performing device-to-device (D2D) communication by
a user equipment in a wireless communication system is disclosed in
the present application. More particularly, the method comprises
the steps of: receiving a discovery signal from a counterpart user
equipment (UE); identifying at least one of information indicating
whether the counterpart UE is located within the coverage area of a
base station and information indicating whether the counterpart UE
is in a connected mode or in an idle mode, all of which are
included in the discovery signal; and performing the D2D
communication with the counterpart UE by using the at least one
identified pierce of information.
Inventors: |
SEO; Hanbyul; (Seoul,
KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
(LG ELECTRONICS INC.) |
Yeongdeungpo-gu, Seoul |
|
KR |
|
|
Assignee: |
LG ELECTRONICS INC.
Seoul
KR
|
Family ID: |
51428497 |
Appl. No.: |
14/766936 |
Filed: |
February 18, 2014 |
PCT Filed: |
February 18, 2014 |
PCT NO: |
PCT/KR2014/001303 |
371 Date: |
August 10, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61769720 |
Feb 26, 2013 |
|
|
|
Current U.S.
Class: |
370/280 |
Current CPC
Class: |
H04W 76/14 20180201;
H04W 72/042 20130101; H04W 72/0413 20130101; H04L 5/14 20130101;
H04W 88/08 20130101; H04W 8/005 20130101 |
International
Class: |
H04W 76/02 20060101
H04W076/02; H04W 72/04 20060101 H04W072/04; H04L 5/14 20060101
H04L005/14 |
Claims
1-10. (canceled)
11. A method for transceiving signals via a Device-to-Device (D2D)
link at a user equipment (UE) in a wireless communication system,
the method comprising; transmitting information for communicating
with another UE on a first channel via the D2D link; and
transmitting and receiving the signals on a second channel via the
D2D link using the information, wherein the information for
communicating with another user equipment includes an indicator
indicating whether the UE is located within a coverage of a base
station or not.
12. The method of claim 11, wherein, if a Time Division Duplex
(TDD) mode is applied to the UE, the information for communicating
with another user equipment further includes information indicating
an uplink/downlink (UL/DL) subframe configuration which is applied
to a serving cell of the UE.
13. The method of claim 11, wherein the second channel is a D2D
data channel.
14. The method of claim 11, wherein the information for
communicating with another UE is transmitted before transmitting
and receiving the signals.
15. The method of claim 11, wherein the information for
communicating with another user equipment further includes
information indicating whether a duplex mode applied to the UE is a
Frequency Division Duplex (FDD) mode or a Time Division Duplex
(TDD) mode.
16. A method for transceiving signals via a Device-to-Device (D2D)
link at a user equipment (UE) in a wireless communication system,
the method comprising; receiving information for communicating with
another UE on a first channel via the D2D link; and receiving and
transmitting the signals on a second channel via the D2D link using
the information, wherein the information for communicating with
another user equipment includes an indicator indicating whether the
another UE is located within a coverage of a base station or
not.
17. The method of claim 16, wherein, if a Time Division Duplex
(TDD) mode is applied to the another UE, the information for
communicating with another user equipment further includes
information indicating an uplink/downlink (UL/DL) subframe
configuration which is applied to a serving cell of the another
UE.
18. The method of claim 16, wherein the second channel is a D2D
data channel.
19. The method of claim 16, wherein the information for
communicating with another UE is received before receiving and
transmitting the signals.
20. The method of claim 16, wherein the information for
communicating with another user equipment further includes
information indicating whether a duplex mode applied to the another
UE is a Frequency Division Duplex (FDD) mode or a Time Division
Duplex (TDD) mode.
Description
TECHNICAL FIELD
[0001] The present invention relates to a wireless communication
system and, more particularly, to a method and apparatus for
transmitting and receiving a discovery signal for device-to-device
(D2D) communication in a wireless communication system.
BACKGROUND ART
[0002] 3GPP LTE (3rd generation partnership project long term
evolution hereinafter abbreviated LTE) communication system is
schematically explained as an example of a wireless communication
system to which the present invention is applicable.
[0003] FIG. 1 is a schematic diagram of E-UMTS network structure as
one example of a wireless communication system. E-UMTS (evolved
universal mobile telecommunications system) is a system evolved
from a conventional UMTS (universal mobile telecommunications
system). Currently, basic standardization works for the E-UMTS are
in progress by 3GPP. E-UMTS is called LTE system in general.
Detailed contents for the technical specifications of UMTS and
E-UMTS refers to release 7 and release 8 of "3rd generation
partnership project; technical specification group radio access
network", respectively.
[0004] Referring to FIG. 1, E-UMTS includes a user equipment (UE),
an eNode B (eNB), and an access gateway (hereinafter abbreviated
AG) connected to an external network in a manner of being situated
at the end of a network (E-UTRAN). The eNode B may be able to
simultaneously transmit multi data streams for a broadcast service,
a multicast service and/or a unicast service.
[0005] One eNode B contains at least one cell. The cell provides a
downlink transmission service or an uplink transmission service to
a plurality of user equipments by being set to one of 1.25 MHz, 2.5
MHz, 5 MHz, 10 MHz, 15 MHz, and 20 MHz of bandwidths. Different
cells can be configured to provide corresponding bandwidths,
respectively. An eNode B controls data transmissions/receptions
to/from a plurality of the user equipments. For a downlink
(hereinafter abbreviated DL) data, the eNode B informs a
corresponding user equipment of time/frequency region on which data
is transmitted, coding, data size, HARQ (hybrid automatic repeat
and request) related information and the like by transmitting DL
scheduling information. And, for an uplink (hereinafter abbreviated
UL) data, the eNode B informs a corresponding user equipment of
time/frequency region usable by the corresponding user equipment,
coding, data size, HARQ-related information and the like by
transmitting UL scheduling information to the corresponding user
equipment. Interfaces for user-traffic transmission or control
traffic transmission may be used between eNode Bs. A core network
(CN) consists of an AG (access gateway) and a network node for user
registration of a user equipment and the like. The AG manages a
mobility of the user equipment by a unit of TA (tracking area)
consisting of a plurality of cells.
[0006] Wireless communication technologies have been developed up
to LTE based on WCDMA. Yet, the ongoing demands and expectations of
users and service providers are consistently increasing. Moreover,
since different kinds of radio access technologies are continuously
developed, a new technological evolution is required to have a
future competitiveness. Cost reduction per bit, service
availability increase, flexible frequency band use, simple
structure/open interface and reasonable power consumption of user
equipment and the like are required for the future
competitiveness.
DISCLOSURE
Technical Problem
[0007] An object of the present invention devised to solve the
problem lies in a method and apparatus for transmitting and
receiving a discovery signal for device-to-device (D2D)
communication in a wireless communication system.
Technical Solution
[0008] The object of the present invention can be achieved by
providing a method of performing device-to-device (D2D)
communication at a user equipment (UE) in a wireless communication
system including receiving a discovery signal from a counterpart
UE, identifying at least one of information as to whether the
counterpart UE is located within coverage of a base station and
information as to whether the counterpart UE is in a connected mode
or in an idle mode, all of which are included in the discovery
signal, and performing D2D communication with the counterpart UE
using the at least one piece of information.
[0009] The performing D2D communication may include stopping D2D
communication in a communication duration between the counterpart
UE and the base station, when the counterpart UE is located within
the coverage of the base station and is in the connected mode.
[0010] The performing D2D communication may include transmitting,
to the base station, a D2D communication request signal for
requesting that the base station assign resources for D2D
communication to the counterpart UE, when the counterpart UE is
located within the coverage of the base station and is in the
connected mode. When the counterpart UE is located within the
coverage of the base station and is in the idle mode, the
counterpart UE may be switched to the connected mode within a
predetermined time and transmits the D2D communication request
signal to the base station.
[0011] When the counterpart UE is located within the coverage of
the base station or is in the connected mode, the discovery signal
may include an identifier of a network connected with the
counterpart UE.
[0012] In another aspect of the present invention, provided herein
is a user equipment (UE) apparatus for performing device-to-device
(D2D) communication in a wireless communication system including a
wireless communication module configured to transmit and receive a
signal to and from a base station or a counterpart UE apparatus of
D2D communication, and a processor configured to process the
signal, wherein the processor controls the wireless communication
module to identify at least one of information as to whether the
counterpart UE apparatus is located within coverage of the base
station and information as to whether the counterpart UE apparatus
is in a connected mode or in an idle mode, all of which are
included in the discovery signal received from the counterpart UE
apparatus and to perform D2D communication with the counterpart UE
apparatus using the at least one piece of information.
[0013] The processor may control the wireless communication module
to stop D2D communication in a communication duration between the
counterpart UE apparatus and the base station, when the counterpart
UE apparatus is located within the coverage of the base station and
is in the connected mode.
[0014] The processor may control the wireless communication module
to transmit, to the base station, a D2D communication request
signal for requesting that the base station assign resources for
D2D communication to the counterpart UE apparatus, when the
counterpart UE apparatus is located within the coverage of the base
station and is in the connected mode. When the counterpart UE
apparatus is located within the coverage of the base station and is
in the idle mode, the counterpart UE apparatus may be switched to
the connected mode within a predetermined time and transmit the D2D
communication request signal to the base station.
Advantageous Effects
[0015] According to embodiments of the present invention, it is
possible to more efficiently transmit a discovery signal for
device-to-device (D2D) communication in a wireless communication
system
[0016] It will be appreciated by persons skilled in the art that
that the effects that can be achieved through the present invention
are not limited to what has been particularly described hereinabove
and other advantages of the present invention will be more clearly
understood from the following detailed description.
DESCRIPTION OF DRAWINGS
[0017] FIG. 1 is a diagram showing a network structure of an
Evolved Universal Mobile Telecommunications System (E-UMTS) as an
example of a wireless communication system.
[0018] FIG. 2 is a diagram showing a control plane and a user plane
of a radio interface protocol architecture between a User Equipment
(UE) and an Evolved Universal Terrestrial Radio Access Network
(E-UTRAN) based on a 3rd Generation Partnership Project (3GPP)
radio access network standard.
[0019] FIG. 3 is a diagram showing physical channels used in a 3GPP
system and a general signal transmission method using the same.
[0020] FIG. 4 is a diagram showing the structure of a downlink
radio frame used in a Long Term Evolution (LTE) system.
[0021] FIG. 5 is a diagram showing the structure of an uplink
subframe used in an LTE system.
[0022] FIG. 6 illustrates a structure of a radio frame in an LTE
TDD system.
[0023] FIG. 7 is a diagram illustrating the concept of
device-to-device (D2D) communication.
[0024] FIG. 8 is a diagram showing an example of generating a D2D
discovery signal according to an embodiment of the present
invention.
[0025] FIG. 9 is a diagram showing an example of performing D2D
communication according to an embodiment of the present
invention.
[0026] FIG. 10 is a diagram showing another example of performing
D2D communication according to an embodiment of the present
invention.
[0027] FIG. 11 is a block diagram of a communication apparatus
according to an embodiment of the present invention.
BEST MODE
[0028] In the following description, compositions of the present
invention, effects and other characteristics of the present
invention can be easily understood by the embodiments of the
present invention explained with reference to the accompanying
drawings. Embodiments explained in the following description are
examples of the technological features of the present invention
applied to 3GPP system.
[0029] In this specification, the embodiments of the present
invention are explained using an LTE system and an LTE-A system,
which is exemplary only. The embodiments of the present invention
are applicable to various communication systems corresponding to
the above mentioned definition. In particular, although the
embodiments of the present invention are described in the present
specification on the basis of FDD, this is exemplary only. The
embodiments of the present invention may be easily modified and
applied to H-FDD or TDD.
[0030] FIG. 2 is a diagram for structures of control and user
planes of radio interface protocol between a 3GPP radio access
network standard-based user equipment and E-UTRAN. The control
plane means a path on which control messages used by a user
equipment (UE) and a network to manage a call are transmitted. The
user plane means a path on which such a data generated in an
application layer as audio data, internet packet data, and the like
are transmitted.
[0031] A physical layer, which is a 1st layer, provides higher
layers with an information transfer service using a physical
channel. The physical layer is connected to a medium access control
layer situated above via a transport channel (trans antenna port
channel). Data moves between the medium access control layer and
the physical layer on the transport channel. Data moves between a
physical layer of a transmitting side and a physical layer of a
receiving side on the physical channel. The physical channel
utilizes time and frequency as radio resources. Specifically, the
physical layer is modulated by OFDMA (orthogonal frequency division
multiple access) scheme in DL and the physical layer is modulated
by SC-FDMA (single carrier frequency division multiple access)
scheme in UL.
[0032] Medium access control (hereinafter abbreviated MAC) layer of
a 2nd layer provides a service to a radio link control (hereinafter
abbreviated RLC) layer, which is a higher layer, on a logical
channel. The RLC layer of the 2nd layer supports a reliable data
transmission. The function of the RLC layer may be implemented by a
function block within the MAC. PDCP (packet data convergence
protocol) layer of the 2nd layer performs a header compression
function to reduce unnecessary control information, thereby
efficiently transmitting such IP packets as IPv4 packets and IPv6
packets in a narrow band of a radio interface.
[0033] Radio resource control (hereinafter abbreviated RRC) layer
situated in the lowest location of a 3rd layer is defined on a
control plane only. The RRC layer is responsible for control of
logical channels, transport channels and physical channels in
association with a configuration, a re-configuration and a release
of radio bearers (hereinafter abbreviated RBs). The RB indicates a
service provided by the 2nd layer for a data delivery between the
user equipment and the network. To this end, the RRC layer of the
user equipment and the RRC layer of the network exchange a RRC
message with each other. In case that there is an RRC connection
(RRC connected) between the user equipment and the RRC layer of the
network, the user equipment lies in the state of RRC connected
(connected mode). Otherwise, the user equipment lies in the state
of RRC idle (idle mode). A non-access stratum (NAS) layer situated
at the top of the RRC layer performs such a function as a session
management, a mobility management and the like.
[0034] A single cell consisting of an eNode B (eNB) is set to one
of 1.25 MHz, 2.5 MHz, 5 MHz, 10 MHz, 15 MHz, and 20 MHz of
bandwidths and then provides a downlink or uplink transmission
service to a plurality of user equipments. Different cells can be
configured to provide corresponding bandwidths, respectively.
[0035] DL transport channels for transmitting data from a network
to a user equipment include a BCH (broadcast channel) for
transmitting a system information, a PCH (paging channel) for
transmitting a paging message, a downlink SCH (shared channel) for
transmitting a user traffic or a control message and the like. DL
multicast/broadcast service traffic or a control message may be
transmitted on the DL SCH or a separate DL MCH (multicast channel).
Meanwhile, UL transport channels for transmitting data from a user
equipment to a network include a RACH (random access channel) for
transmitting an initial control message, an uplink SCH (shared
channel) for transmitting a user traffic or a control message. A
logical channel, which is situated above a transport channel and
mapped to the transport channel, includes a BCCH (broadcast
channel), a PCCH (paging control channel), a CCCH (common control
channel), a MCCH (multicast control channel), a MTCH (multicast
traffic channel) and the like.
[0036] FIG. 3 is a diagram for explaining physical channels used
for 3GPP system and a general signal transmission method using the
physical channels.
[0037] If a power of a user equipment is turned on or the user
equipment enters a new cell, the user equipment may perform an
initial cell search job for matching synchronization with an eNode
B and the like [S301]. To this end, the user equipment may receive
a primary synchronization channel (P-SCH) and a secondary
synchronization channel (S-SCH) from the eNode B, may be
synchronized with the eNode B and may then obtain information such
as a cell ID and the like. Subsequently, the user equipment may
receive a physical broadcast channel from the eNode B and may be
then able to obtain intra-cell broadcast information. Meanwhile,
the user equipment may receive a downlink reference signal (DL RS)
in the initial cell search step and may be then able to check a DL
channel state.
[0038] Having completed the initial cell search, the user equipment
may receive a physical downlink shared control channel (PDSCH)
according to a physical downlink control channel (PDCCH) and an
information carried on the physical downlink control channel
(PDCCH). The user equipment may be then able to obtain detailed
system information [S302].
[0039] Meanwhile, if a user equipment initially accesses an eNode B
or does not have a radio resource for transmitting a signal, the
user equipment may be able to perform a random access procedure to
complete the access to the eNode B [S303 to S306]. To this end, the
user equipment may transmit a specific sequence as a preamble on a
physical random access channel (PRACH) [S303/S305] and may be then
able to receive a response message on PDCCH and the corresponding
PDSCH in response to the preamble [S304/S306]. In case of a
contention based random access procedure (RACH), it may be able to
additionally perform a contention resolution procedure.
[0040] Having performed the above mentioned procedures, the user
equipment may be able to perform a PDCCH/PDSCH reception [S307] and
a PUSCH/PUCCH (physical uplink shared channel/physical uplink
control channel) transmission [S308] as a general uplink/downlink
signal transmission procedure. In particular, the user equipment
receives a DCI (downlink control information) on the PDCCH. In this
case, the DCI contains such a control information as an information
on resource allocation to the user equipment. The format of the DCI
varies in accordance with its purpose.
[0041] Meanwhile, control information transmitted to an eNode B
from a user equipment via UL or the control information received by
the user equipment from the eNode B includes downlink/uplink
ACK/NACK signals, CQI (Channel Quality Indicator), PMI (Precoding
Matrix Index), RI (Rank Indicator) and the like. In case of 3GPP
LTE system, the user equipment may be able to transmit the
aforementioned control information such as CQI/PMI/RI and the like
on PUSCH and/or PUCCH.
[0042] FIG. 4 illustrates exemplary control channels included in a
control region of a subframe in a DL radio frame.
[0043] Referring to FIG. 4, a subframe includes 14 OFDM symbols.
The first one to three OFDM symbols of a subframe are used for a
control region and the other 13 to 11 OFDM symbols are used for a
data region according to a subframe configuration. In FIG. 5,
reference characters R1 to R4 denote RSs or pilot signals for
antenna 0 to antenna 3. RSs are allocated in a predetermined
pattern in a subframe irrespective of the control region and the
data region. A control channel is allocated to non-RS resources in
the control region and a traffic channel is also allocated to
non-RS resources in the data region. Control channels allocated to
the control region include a Physical Control Format Indicator
Channel (PCFICH), a Physical Hybrid-ARQ Indicator Channel (PHICH),
a Physical Downlink Control Channel (PDCCH), etc.
[0044] The PCFICH is a physical control format indicator channel
carrying information about the number of OFDM symbols used for
PDCCHs in each subframe. The PCFICH is located in the first OFDM
symbol of a subframe and configured with priority over the PHICH
and the PDCCH. The PCFICH includes 4 Resource Element Groups
(REGs), each REG being distributed to the control region based on a
cell Identifier (ID). One REG includes 4 Resource Elements (REs).
An RE is a minimum physical resource defined by one subcarrier by
one OFDM symbol. The PCFICH is set to 1 to 3 or 2 to 4 according to
a bandwidth. The PCFICH is modulated in Quadrature Phase Shift
Keying (QPSK).
[0045] The PHICH is a physical Hybrid-Automatic Repeat and request
(HARQ) indicator channel carrying an HARQ ACK/NACK for a UL
transmission. That is, the PHICH is a channel that delivers DL
ACK/NACK information for UL HARQ. The PHICH includes one REG and is
scrambled cell-specifically. An ACK/NACK is indicated in one bit
and modulated in Binary Phase Shift Keying (BPSK). The modulated
ACK/NACK is spread with a Spreading Factor (SF) of 2 or 4. A
plurality of PHICHs mapped to the same resources form a PHICH
group. The number of PHICHs multiplexed into a PHICH group is
determined according to the number of spreading codes. A PHICH
(group) is repeated three times to obtain a diversity gain in the
frequency domain and/or the time domain.
[0046] The PDCCH is a physical DL control channel allocated to the
first n OFDM symbols of a subframe. Herein, n is 1 or a larger
integer indicated by the PCFICH. The PDCCH occupies one or more
CCEs. The PDCCH carries resource allocation information about
transport channels, PCH and DL-SCH, a UL scheduling grant, and HARQ
information to each UE or UE group. The PCH and the DL-SCH are
transmitted on a PDSCH. Therefore, an eNB and a UE transmit and
receive data usually on the PDSCH, except for specific control
information or specific service data.
[0047] Information indicating one or more UEs to receive PDSCH data
and information indicating how the UEs are supposed to receive and
decode the PDSCH data are delivered on a PDCCH. For example, on the
assumption that the Cyclic Redundancy Check (CRC) of a specific
PDCCH is masked by Radio Network Temporary Identity (RNTI) "A" and
information about data transmitted in radio resources (e.g. at a
frequency position) "B" based on transport format information (e.g.
a transport block size, a modulation scheme, coding information,
etc.) "C" is transmitted in a specific subframe, a UE within a cell
monitors, that is, blind-decodes a PDCCH using its RNTI information
in a search space. If one or more UEs have RNTI "A", these UEs
receive the PDCCH and receive a PDSCH indicated by "B" and "C"
based on information of the received PDCCH.
[0048] A basic resource unit of a DL control channel is an REG. The
REG includes four contiguous REs except for REs carrying RSs. A
PCFICH and a PHICH include 4 REGs and 3 REGs, respectively. A PDCCH
is configured in units of a Control Channel Element (CCE), each CCE
including 9 REGs.
[0049] FIG. 5 illustrates a structure of a UL subframe in the LTE
system.
[0050] Referring to FIG. 5, a UL subframe may be divided into a
control region and a data region. A Physical Uplink Control Channel
(PUCCH) including Uplink Control Information (UCI) is allocated to
the control region and a Physical uplink Shared Channel (PUSCH)
including user data is allocated to the data region. The middle of
the subframe is allocated to the PUSCH, while both sides of the
data region in the frequency domain are allocated to the PUCCH.
Control information transmitted on the PUCCH may include an HARQ
ACK/NACK, a CQI representing a downlink channel state, an RI for
MIMO, a Scheduling Request (SR) requesting UL resource allocation.
A PUCCH for one UE occupies one RB in each slot of a subframe. That
is, the two RBs allocated to the PUCCH are frequency-hopped over
the slot boundary of the subframe. Particularly, PUCCHs with m=0,
m=1, m=2, and m=3 are allocated to a subframe in FIG. 5.
[0051] FIG. 6 illustrates a structure of a radio frame in an LTE
TDD system. In the LTE TDD system, a radio frame includes two half
frames, and each half frame includes four normal subframes each
including two slots, and a special subframe including a downlink
pilot time slot (DwPTS), a guard period (GP), and an uplink pilot
time slot (UpPTS).
[0052] In the special subframe, the DwPTS is used for initial cell
search, synchronization, or channel estimation in a UE. The UpPTS
is used for channel estimation in an eNB and uplink transmission
synchronization of a UE. That is, the DwPTS is used for downlink
transmission and the UpPTS is used for uplink transmission. In
particular, the UpPTS is used for transmission of a PRACH preamble
or SRS. In addition, the GP is a period for removing interference
generated in uplink due to multipath delay of a downlink signal
between uplink and downlink.
[0053] Currently, in an LTE TDD system, the special subframe is
configured as a total of 10 configurations as shown in Table 1
below.
TABLE-US-00001 TABLE 1 Normal cyclic prefix in downlink Extended
cyclic prefix in downlink UpPTS UpPTS Normal Extended Normal
Extended Special subframe cyclic prefix cyclic prefix cyclic prefix
cyclic prefix configuration DwPTS in uplink in uplink DwPTS in
uplink in uplink 0 6592 T.sub.s 2192 T.sub.s 2560 T.sub.s 7680
T.sub.s 2192 T.sub.s 2560 T.sub.s 1 19760 T.sub.s 20480 T.sub.s 2
21952 T.sub.s 23040 T.sub.s 3 24144 T.sub.s 25600 T.sub.s 4 26336
T.sub.s 7680 T.sub.s 4384 T.sub.s 5120 T.sub.s 5 6592 T.sub.s 4384
T.sub.s 5120 T.sub.s 20480 T.sub.s 6 19760 T.sub.s 23040 T.sub.s 7
21952 T.sub.s -- -- -- 8 24144 T.sub.s -- -- --
Meanwhile, in an LTE TDD system, a UL/DL configuration is shown in
Table 2 below.
TABLE-US-00002 TABLE 2 Uplink- Dowlink-to- downlink Uplink
configura- Switch-point Subframe number tion periodicity 0 1 2 3 4
5 6 7 8 9 0 5 ms D S U U U D S U U U 1 5 ms D S U U D D S U U D 2 5
ms D S U D D D S U D D 3 10 ms D S U U U D D D D D 4 10 ms D S U U
D D D D D D 5 10 ms D S U D D D D D D D 6 5 ms D S U U U D S U U
D
[0054] In Table 2 above, D, U, and S refer to a downlink subframe,
an uplink subframe, and the special subframe. In addition, Table 2
also shows downlink-to-uplink switch-point periodicity in an
uplink/downlink subframe configuration in each system.
[0055] FIG. 7 shows the concept of D2D communication.
[0056] Referring to FIG. 7, in device-to-device (D2D) communication
in which a UE directly performs communication with another UE, an
eNB may transmit a scheduling message indicating D2D transmission
and reception. A UE participating in D2D communication receives the
D2D scheduling message from the eNB and performs transmission and
reception operation indicated by the D2D scheduling message. Here,
the UE means a user terminal and a network entity such as an eNB
may also be regarded as a UE when the network entity transmits and
receives a signal according to a communication method between UEs.
Hereinafter, a link between UEs is referred to as a D2D link and a
link between a UE and an eNB is referred to as an NU link.
[0057] For D2D operation, a UE performs a discovery procedure of
determining whether a counterpart UE of D2D communication is
located in a D2D communication area. Such a discovery procedure
includes transmitting a unique discovery signal for identifying
each UE and determining that the UE, which has transmitted the
discovery signal, is located at a neighboring position when a
neighboring UE detects the discovery signal. That is, each UE
determines whether a counterpart UE of D2D communication is located
at a neighboring position via the discovery procedure and then
performs D2D communication for transmitting and receiving user
data.
[0058] D2D discovery and D2D communication may be performed between
UEs, which are connected to an eNB in eNB coverage to perform
communication, and between UEs located outside eNB coverage without
connection to the eNB. Additionally, one of two UEs connected via
one D2D link may be located within eNB coverage and the other UE
may be located outside eNB coverage. That is, D2D discovery and D2D
communication may be performed between a UE located within eNB
coverage and a UE located outside eNB coverage.
[0059] Whether a UE is located within eNB coverage may be
determined using reception quality of a reference signal
transmitted by an eNB. More specifically, when the reference signal
received power (RSRP) or reference signal received quality (RSRQ)
of a reference signal of an arbitrary eNB measured by a UE is equal
to or less than a predetermined level, it may be determined that
the UE is located outside eNB coverage.
[0060] The UE located within eNB coverage may be divided into a UE
in an idle mode and a UE in a connected mode. The UE in the
connected mode means a UE for currently transmitting and receiving
data to and from the eNB or a UE which can start data transmission
and reception to and from the eNB via scheduling of the eNB. In
contrast, the UE in the idle mode means a UE which is located
within eNB coverage but does not currently perform data
transmission and reception to and from the eNB and should be
switched to the connected mode via a process of connecting the UE
and the eNB in order to transmit and receive data between the UE
and the eNB.
[0061] The UE in the connected mode should maintain an NU link for
performing communication with the eNB and a D2D link for performing
communication with another UE. For example, the NU link may operate
using a series of time resources and the D2D link may operate using
other time resources. In other words, the UE in the connected mode
has restraints on time resources for performing D2D operation.
[0062] In contrast, the UE in the idle mode does not need to always
perform communication with the eNB but should periodically receive
paging indicating that there is data traffic from the eNB.
Accordingly, the UE in the idle mode has restraints on time
resources for performing D2D operation, similarly to the UE in the
connected mode and the total time resources may be divided into
resources for the NU link and resources for the D2D link. Resources
used to transmit paging at the eNB and resources used to perform
D2D operation at the UE are distinguished in terms of frequency
and, when the UE can receive a signal from the eNB and, at the same
time, can perform D2D operation using different frequency
resources, D2D communication may be performed using all time
resources without distinguishing between operations of the two
links in terms of time.
[0063] As described above, the UE finds the counterpart UE of D2D
communication via the discovery procedure and then attempts D2D
communication with the counterpart UE. At this time, when the
counterpart UE is located within eNB coverage and performs NU link
communication using predetermined time resources, the UE cannot
perform D2D communication with the counterpart UE while the
counterpart UE performs NU link communication. Accordingly, such
time resources are not used for D2D communication, thereby reducing
unnecessary power consumption. When the counterpart UE is located
outside eNB coverage or when the counterpart UE is located within
eNB coverage but restraints on time resources used to transmit and
receive a D2D signal are not imposed, D2D communication is
efficiently performed using as many time resources as possible.
[0064] In order to appropriately select time resources used for D2D
communication depending on whether the counterpart UE is located
within eNB coverage or whether the counterpart UE is connected to
the network, the present invention proposes use of network related
information when the UE generates, transmits and receives the
discovery signal.
[0065] FIG. 8 is a diagram showing an example of generating a D2D
discovery signal according to an embodiment of the present
invention. Referring to FIG. 8, information on a network, to which
a UE is connected, is applied as a variable used to generate a D2D
discovery signal.
[0066] Hereinafter, a detailed example of generating and
transmitting a discovery signal at a UE according to the present
invention will be described.
[0067] First, a variable applied when each UE generates a discovery
signal may include whether each UE is located within eNB coverage.
That is, even in the same UE, the sequence, time/frequency
resources, transmit power, etc. of a discovery signal are changed
depending on whether the UE is located within or outside eNB
coverage. For example, when the sequence of the discovery signal is
generated, bits 0 and 1 may be respectively applied as values for
initializing a sequence generator when the UE is located within and
outside eNB coverage.
[0068] Alternatively, as a method of providing additional
information, a variable used to generate a discovery signal at each
UE may include whether each UE is in the connected mode. For
example, when the UE generates the discovery signal, whether the UE
is in the connected mode may be used instead of whether the UE is
located within eNB coverage. This method is suitable when
restraints on time resources used for D2D operations are not
imposed because the UE is in the idle mode although the UE is
located within coverage. That is, the UE which is located within
coverage and is in the idle mode and the UE located outside
coverage are not distinguished.
[0069] Operation for not distinguishing the UE which is located
within coverage and is in the idle mode and the UE located outside
coverage is suitable when the UE in the idle mode performs eNB
signal reception operation via resources separated from those of
D2D operation in the frequency domain, e.g., when a signal is
received from the eNB in a downlink band and D2D operation is
performed in an uplink band in an FDD system. This is because D2D
signal transmission and reception in the uplink band does not have
influence on eNB signal reception.
[0070] As another example, the UE located within coverage may use
information as to whether the UE is in the connected mode or in the
idle mode, when generating the discovery signal, in addition to
information indicating that the UE is located within eNB coverage.
This method is suitable when the UE which is located within
coverage and is in the idle mode has restraints on time resources
used for D2D operation. Operation for distinguishing between the UE
which is located within coverage and is in the idle mode and the UE
located outside coverage is suitable when the UE in the idle mode
performs eNB signal reception operation and D2D operation in the
same frequency domain, e.g., when the eNB signal is received via a
downlink subframe of a TDD system and D2D operation is performed
via an uplink subframe. This is because D2D signal transmission in
the frequency band of the TDD system may cause interference with
eNB signal reception in the same frequency band.
[0071] When the above-described examples are used, information used
to generate the discovery signal may be changed according to a
duplex mode of the UE. For example, whether the UE is in the
connected mode may be used in the FDD system and whether the UE is
located within eNB coverage may be used in the TDD system.
[0072] According to the above-described method of generating the
discovery signal, each UE may determine whether the counterpart UE
of D2D communication is located within eNB coverage and/or is in
the connected mode. Based on this information, the UE may perform
appropriate operation suitable for the state of the counterpart UE
when starting D2D communication.
[0073] For example, when it is determined that predetermined time
resources are not used for D2D communication because the
counterpart UE is located within coverage or is in the connected
mode, the UE may not perform D2D operation via those resources but
may transmit D2D signal to the counterpart UE using the other time
resources. When restraints on the time resources for D2D
communication are not imposed because the counterpart UE is located
outside eNB coverage or is in the idle mode, the UE may transmit
the D2D signal to the counterpart UE using arbitrary time
resources.
[0074] FIG. 9 is a diagram showing an example of performing D2D
communication according to an embodiment of the present invention.
In particular, in FIG. 9, UE1 performs D2D communication with UE2
and UE3, UE2 has restraints on D2D time resources and UE3 does not
have restraints on D2D time resources.
[0075] Although not shown in FIG. 9, in a TDD system, in time
resources having restraints on D2D communication with UE2, D2D
signal communication may be restricted in order to protect the NU
link operation of UE2. Alternatively, in an FDD system, since D2D
signal transmission to UE2 is impossible but the signal does not
have influence on the NU link operation of UE2, the D2D signal may
be transmitted to the UE without restraints, such as UE3.
[0076] Referring to FIG. 9, UE1 may perform D2D communication with
another UE without restraints via resources, in which D2D
communication with UE2 is restricted, with lower transmit power,
e.g., transmit power obtained by subtracting a predetermined offset
from general D2D transmit power or maximum transmit power less than
maximum power of general D2D transmission, while protecting the NU
link operation of UE2.
[0077] In addition, when it is determined that an instruction of
the eNB is necessary for D2D communication because the counterpart
UE is located within eNB coverage or is in the connected mode, the
UE may transmit a D2D communication request signal to the eNB. That
is, the UE transmits a D2D communication request signal to the eNB
and enables the eNB to assign resources to perform D2D operation
with the counterpart UE using predetermined time resources. This is
referred to as a first D2D communication method. In contrast, the
UE which is located within eNB coverage and is in the idle mode may
perform D2D communication while maintaining the idle mode without
the direct instruction of the eNB (this is referred to as a second
D2D communication method and the same is true even when the UE is
located outside eNB coverage) or the UE in the idle mode may not
perform D2D communication but may always perform D2D communication
according to the direct instruction of the eNB after being switched
to the connected mode.
[0078] D2D request signal may include the identifier of the
counterpart UE, the communication state of the UE, the quality of
the discovery signal of the detected counterpart UE, the amount of
resources necessary for D2D communication, etc. Since the request
for D2D communication from the eNB may be made only when the UE is
in the connected mode, the UE which is located within eNB coverage
and is in the idle mode may transmit the D2D communication request
signal after being switched to the connected mode.
[0079] When the UE is located outside eNB coverage, the UE cannot
request D2D communication from the eNB. Therefore, the UE may
directly request D2D communication from the counterpart UE or wait
until the counterpart UE starts D2D communication. In particular,
when the counterpart UE is located within eNB coverage or is in the
connected mode, the UE may wait until the counterpart UE starts D2D
communication without interfering with NU link communication.
[0080] When the UE waits until the counterpart UE starts D2D
communication, a timer may be set and the UE waits until the timer
ends. When the UE does not start D2D communication before the timer
ends, the UE may directly attempt D2D communication with the
counterpart UE or abandon D2D communication with the counterpart UE
and attempt communication with another UE.
[0081] In addition, when it is determined that the instruction of
the eNB is unnecessary for D2D communication because the
counterpart UE is located outside coverage or is in the idle mode,
the UE may directly start D2D communication with the counterpart
UE. This is referred to as a second D2D communication method. When
information on the idle mode is included in the discovery signal,
one of the first communication method and the second communication
method may be selected.
[0082] In the above cases, operation for preparing D2D signal
reception at the counterpart UE may be changed according to the
state of the counterpart UE.
[0083] When the instruction of the eNB is necessary for D2D
communication because the counterpart UE is located within eNB
coverage or is in the connected mode, the counterpart UE may not
prepare D2D communication with the UE until the instruction of the
eNB is received, thereby reducing unnecessary power consumption. In
contrast, when the instruction of the eNB is unnecessary for D2D
communication because the counterpart UE is located outside eNB
coverage or is in the idle mode, D2D communication with the UE
should be prepared via arbitrary resources, in which D2D
communication is possible, such that the UE can directly start D2D
communication.
[0084] As another example of information used to generate, transmit
and receive the discovery signal, attribute information of a
network, to which the UE belongs to, may be included in the case of
the UE located within coverage or the UE in the connected mode.
Using this information, a counterpart D2D UE located outside eNB
coverage or located in another cell may determine the attribute of
each UE upon NU link operation via the discovery procedure.
[0085] As an example of information on a network used to generate,
transmit and receive discovery signal, the ID of a network, to
which each UE belongs, may be included as information used to
generate, transmit and receive the discovery signal. The ID of the
network may be the ID of a cell, to which the network belongs, the
ID of a public land mobile network (PLMN) or the ID of a cell
cluster composed of a series of cells.
[0086] More specifically, the cell cluster may be set equally to a
paging group or a tracking area which is a criterion for updating
the position of the UE when the UE moving in the idle mode or a
group of cells in which D2D communication is possible may be a
separately defined D2D cell cluster. Cells belong to one D2D cell
cluster are time synchronized and may exchange a signal via a
backhaul link.
[0087] Each UE may identify network information of the counterpart
UE and perform appropriate D2D communication. For example, when the
counterpart UE belongs to the same cell or the same D2D cell
cluster, the UE determines that operation or scheduling of the
network in which mutual D2D communication is performed is possible
and performs a series of processes for D2D communication. In
contrast, when it is determined that the counterpart UE belongs to
a different cell or a different D2D cell cluster, the UE may
determine that operation of the network for D2D communication
between UEs is impossible and may not perform D2D
communication.
[0088] As another example, when the counterpart UE belongs to the
same cell or the same D2D cell cluster, the UE determines that
mutual D2D communication may be performed without the instruction
of the network and immediately performs D2D communication. In
contrast, when it is determined that the counterpart UE belongs to
a different cell or a different D2D cell cluster, the UE may
determine that D2D communication between the UEs requires an
appropriate advance preparation process of the network, transmit
D2D request information to the eNB and perform D2D communication
according to the instruction of the eNB.
[0089] As another example, when the counterpart UE belongs to the
same cell or the same D2D cell cluster, the UE determines that two
UEs belonging to the D2D link can be controlled by one controller
and performs D2D communication according to the direct instruction
of the eNB. In contrasts, when it is determined that the
counterpart UE belongs to a different cell or a different D2D cell
cluster, the UE determines that the UEs cannot be controlled by the
controller of the network and performs the same procedure as
performing D2D communication with the UE located outside coverage.
For example, D2D communication may be performed without
transmission of D2D communication request information to the eNB or
without the direct instruction of the eNB.
[0090] The network divides D2D resources into a plurality of
resources in advance, that is, resources for D2D with the UE
belonging to the same cell or (or the same D2D cell cluster),
resources for D2D with the UE belonging to a different cell (or a
difference D2D cell cluster) and/or resources for D2D with the UE
located outside coverage, and enables each UE to select appropriate
resources according to the state of the counterpart UE.
[0091] Parameters for transmit power of D2D communication may be
divided into D2D communication with the UE belonging to the same
cell or (or the same D2D cell cluster), D2D communication with the
UE belonging to a different cell (or a different D2D cell cluster)
and/or D2D communication with the UE located outside coverage and
enables each UE to select appropriate resources according to the
state of the counterpart UE.
[0092] As an example of other information used to generate,
transmit and receive the discovery signal, information on the
location and amount of resources used or likely to be used by the
UE as the NU link may be included. That is, information as to how
many resources are used or where resources used for D2D
communication are located may be used to generate, transmit and
receive the discovery signal. Each UE notifies the counterpart UE
of resources in which D2D communication is possible and enables the
counterpart UE to identify a location where D2D communication may
be performed, thereby reducing unnecessary interference and power
consumption due to communication performed at a location where D2D
communication is impossible.
[0093] FIG. 10 is a diagram showing another example of performing
D2D communication according to an embodiment of the present
invention.
[0094] Referring to FIG. 10, UE1 identifies that UE2 uses three NU
links among five time domains and UE3 uses one NU link among five
time domains, before performing D2D communication with UE2 and UE3
and performs D2D communication using the time domains in which D2D
communication is possible.
[0095] In particular, the eNB may determine and send which
resources are used for D2D communication and are used to generate
the discovery signal to the UE via a higher layer signal such as
radio resource control (RRC) or system information.
[0096] In an FDD system, since the UE in the idle mode receives
only the downlink signal from the eNB and does not have restraints
on D2D communication in the uplink band, the counterpart UE may be
informed that all time resources are used for D2D communication. In
contrast, in a TDD system, the UE may use uplink/downlink
configuration information used by the cell, to which the UE
belongs, in order to enable the counterpart UE located in another
cell or located outside coverage to identify a domain for receiving
the downlink signal transmitted by the eNB and prevent interference
with reception of the downlink signal.
INDUSTRIAL APPLICABILITY
[0097] Although an example in which a method and apparatus for
transmitting and receiving a discover signal for D2D communication
in a wireless communication system is applied to a 3GPP LTE system
is described, the present invention is applicable to various
wireless communication systems in addition to the 3GPP LTE
system.
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